What do you call the phenomenon when you have a different concentration of materials on the inside and the outside of the cell?

This is a concentration gradient. These different levels of a substance between the cell and its environment allow for (facilitated) diffusion and osmosis to occur. The different types of movement are based upon what the substances are on the two sides of the cell. Facilitated diffusion and basic diffusion are based upon non-water substances moving across the gradient while osmosis is the movement of water into and outside the cell.